Crystal Structure of a Charge Engineered Human Lysozyme Having Enhanced Bactericidal Activity

• Published in: PloS one Vol. 6; no. 3; p. e16788
• Main Authors: Gill, Avinash, Scanlon, Thomas C., Osipovitch, Daniel C., Madden, Dean R., Griswold, Karl E.
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 07.03.2011; Public Library of Science (PLoS)
• Subjects: Actins - metabolism; Amino acids; Anti-Bacterial Agents - chemistry; Anti-Bacterial Agents - metabolism; Anti-Bacterial Agents - pharmacology; Antibacterial activity; Antibacterial agents; Automation; Bacteria; Bacterial infections; Bactericidal activity; Biocatalysis - drug effects; Biochemistry; Biology; Biopolymers; Catalysis; Cellular biology; Chemical compounds; Chronic obstructive pulmonary disease; Collaboration; Computational chemistry; Crystal structure; Crystallography; Crystallography, X-Ray; Cystic fibrosis; Deactivation; Deoxyribonucleic acid; DNA; Drug resistance; Electrostatic properties; Engineering; Engineering schools; Enzyme Stability - drug effects; Enzymes; Health aspects; Humans; Immune clearance; Immune system; Inactivation; Infection; Infections; Innate immunity; Ligands; Lysozyme; Microbial drug resistance; Models, Molecular; Mortality; Muramidase - antagonists & inhibitors; Muramidase - chemistry; Muramidase - metabolism; Muramidase - pharmacology; Mutant Proteins - chemistry; Mutation; Pharmacology; Pneumonia; Protein Engineering; Protein Processing, Post-Translational - drug effects; Proteins; Residues; Respiratory tract; Sequence Analysis, Protein; Solvents; Static Electricity; Structural stability; Surface active agents; United States > US; New Hampshire
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0016788

Human lysozyme is a key component of the innate immune system, and recombinant forms of the enzyme represent promising leads in the search for therapeutic agents able to treat drug-resistant infections. The wild type protein, however, fails to participate effectively in clearance of certain infections due to inherent functional limitations. For example, wild type lysozymes are subject to electrostatic sequestration and inactivation by anionic biopolymers in the infected airway. A charge engineered variant of human lysozyme has recently been shown to possess improved antibacterial activity in the presence of disease associated inhibitory molecules. Here, the 2.04 Å crystal structure of this variant is presented along with an analysis that provides molecular level insights into the origins of the protein's enhanced performance. The charge engineered variant's two mutated amino acids exhibit stabilizing interactions with adjacent native residues, and from a global perspective, the mutations cause no gross structural perturbations or loss of stability. Importantly, the two substitutions dramatically expand the negative electrostatic potential that, in the wild type enzyme, is restricted to a small region near the catalytic residues. The net result is a reduction in the overall strength of the engineered enzyme's electrostatic potential field, and it appears that the specific nature of this remodeled field underlies the variant's reduced susceptibility to inhibition by anionic biopolymers.